The power adapter is an essential electrical apparatus for providing required power to various electronic appliance or informational product, such as notebook, to work. Accompanying with the tendency of minimizing the volume of the electronic appliance or informational product, the power adapter is also designed and developed in small size and with high power efficiency. Accordingly, it becomes more and more important for the manufacturer to deal with the issue of heat dissipation of the power adapter. Generally, there are many electronic devices and electromagnetic devices, such as transformer, disposed on a printed circuit board of the power adapter. These devices will generate a great amount of heat that may cause the internal temperature of the power adapter to be higher and higher, when these devices operate. If the heat is accumulated within the interior of the power adapter and can't be removed efficiently, it will influence the operation efficiency of the power adapter.
Referring to FIG. 1, a conventional heat sink assembly disposed on a printed circuit board of a power adapter is shown. In FIG. 1, the power adapter comprises a printed circuit board 11 having a plurality of electronic devices 12 and one or more electromagnetic devices 13, such as transformers, thereon. These electronic devices 12 and electromagnetic devices 13 can perform the power-conversion operation. Due to the limited space in the power adaptor, a heat sink assembly for efficiently transferring the heat generated from these electromagnetic devices 13 on the printed circuit board 11 to the case (not shown) of the power adapter is needed. A traditional heat sink assembly generally comprises a first heat-dissipating piece 141 disposed above the electromagnetic device 13 and a second heat-dissipating piece 142 disposed on the edge of the printed circuit board 11 and coupled with the first heat-dissipating piece 141. The first heat-dissipating piece 141 can transfer the heat generated from the electromagnetic device 13 to the second heat-dissipating piece 142 on the edge of the printed circuit board 11. Therefore, the heat generated from the top of the electromagnetic device 13 can be transferred from the interior of the power adapter to the case of the power adapter.
As we known, the printed circuit board 11 is usually made of plastic material so that the printed circuit board 11 is a bad heat conductor. Therefore, when the electromagnetic device 13 which is disposed directly on the printed circuit board 11 works, the heat generated from the bottom of the electromagnetic devices 13 is hard to be dissipated away the printed circuit board 11. Although there is a heat-dissipating piece 141 disposed above the electromagnetic device 13, the heat generated from the bottom of the electromagnetic device 13 is hard to be transferred away the printed circuit board 11 via the first heat-dissipating pieces 141 and the second heat-dissipating piece 142. Therefore, it is unable to overcome the problem of dissipating the heat between the printed circuit board 11 and the electromagnetic device 13. Additionally, it is unavoidable that there will be an air gap formed between the electromagnetic device 13 and the printed circuit board 11 when the electromagnetic device 13 is disposed on the printed circuit board 11. Because the air gap formed between the electromagnetic device 13 and the printed circuit board 11 is also unfavorable for the heat dissipation between the electromagnetic device 13 and the printed circuit board 11, it will result in the partial inequality of temperature inside the power adaptor and influence the operation efficiency of the power adapter.
In view of foregoing problems, what is needed is to develop a heat sink assembly that can transfer the heat generated from the electromagnetic device on the printed circuit board to the case of the power adapter effectively. The present invention can satisfy these needs.